1. Field of the Invention
The present invention relates to a light emitting diode and more particularly to a light emitting diode which enhances a scattering of light produced by a light emitting element to produce a uniform, bright illumination in a wide range of angle.
2. Description of the Prior Art
An example of a known conventional light emitting diode is shown in FIG. 1 (see Japanese Patent Disclosure No. 2000-124507). This light emitting diode 1 includes a substrate 2, a pair of electrodes 3a, 3b formed on both sides of the substrate 2, a light emitting element 4 disposed on the substrate 2, bonding wires 5 electrically connecting the light emitting element 4 to the paired electrodes 3a, 3b, and a resin sealant 6 provided on the substrate 2 to seal the light emitting element 4 and the bonding wires 5. Small light scattering particles 7 are dispersed in the entire resin sealant 6 to scatter light and thereby increase the brightness of light produced.
The light emitting diode 1 constructed as described above, however, has the following drawback. Since the light scattering particles 7 are dispersed uniformly in a whole interior of the resin sealant 6, an upper surface of the resin sealant 6 (light projecting surface 8) opposing a light emitting surface (upper surface) of the light emitting element 4 has an improved brightness because of the light scattering by the light scattering particles 7, whereas side surfaces 9 of the resin sealant 6 that do not face the light emitting surface of the light emitting element 4 have a small light scattering effect by the light scattering particles 7 and therefore a low brightness. It is therefore not possible to produce a uniform, bright illumination in a wide range of angle.
An object of the present invention is to provide a light emitting diode which can enhance the scattering of light produced by a light emitting element to improve a brightness not only at an upper surface but also at side surfaces of a sealant covering the light emitting element, thereby providing a high, uniform brightness in a wider range of angle.
To achieve the above objective, a light emitting diode of the present invention comprises: a substrate; a pair of electrodes provided on the substrate; a light emitting element mounted on the substrate and electrically connected to the electrodes; a sealant provided on the substrate to seal the electrodes and the light emitting element; and a light scattering layer formed on an outermost layer of at least one surface of the sealant.
Since the light scattering layer is formed on the outermost layer of the sealant as described above, the light produced by the light emitting element is greatly refracted by the light scattering layer and rays of light reflected back into the interior of the sealant are also scattered inside the sealant, resulting in an enhanced light scattering action. This improves the luminance level not only at the upper surface of the sealant but also at its side surfaces, thus producing a bright, uniform illumination in a wide range of angle.
In one embodiment, the sealant is formed of a resin material which is transparent or has a light permeability, and the light scattering layer is formed of a paint film having a large number of light scattering particles dispersed therein or of a sheet member having a large number of light scattering particles mixed therein. The paint film is formed on the surface of the sealant by printing, and the sheet member is formed on the surface of the sealant by bonding.
The light scattering particles dispersed in the light scattering layer are fine particles of silicon dioxide or titanium oxide. Any desired luminance level can be obtained by adjusting a diameter and an amount of fine particles to be dispersed according to the use of the light emitting diode.
The light scattering particles are projected from the surface of the light scattering layer to form many protrusions and recesses in the surface, i.e., roughen or undulate the surface, to further enhance the light scattering action.
Such a light scattering layer is formed, for example, on the light projecting surface of the sealant which opposes the light emitting surface of the light emitting element. With the light scattering layer provided on the light projecting surface of the sealant, the light emitted from the light emitting surface of the light emitting element can be effectively refracted and reflected, resulting in an enhanced scattering of light in a wide range of angle.